The present invention relates to a method and an apparatus for recording information on an information recording medium by directing an energy beam to the medium to melt its recording film, and to the information recording medium used by the method. More particularly, the present invention relates to a method and an apparatus for recording information on phase change disks such as a DVD-RAM and a DVD-RW, and to an information recording medium used for the method.
In the description of the present invention, the information recording medium described above is mentioned as a phase change optical disk or simply as an optical disk. However, the present invention applies to any information recording medium on which information is recorded by directing an energy beam to the medium to heat and melt its recording film in order to change the atomic arrangement. Therefore, regardless of the shape of an information recording medium, the present invention is applicable also to a method and an apparatus for recording information on non-circular information recording media such as an optical card, and to an information recording medium used for the method.
In addition, the energy beam described above is sometimes mentioned simply as a laser beam or as a light. However, any energy beam capable of generating heat on an information recording medium to melt its recording medium may be used in the present invention as described above. Furthermore, although a red laser (645 nm to 660 nm of wavelength) is used in the method and the apparatus according to the present invention, the present invention is applicable also to a high-density optical disk using a relatively shorter wavelength laser, such as a blue laser and a purple laser.
Recently, phase change optical disks such as a 2.6 GB DVD-RAM, capable of reproducing information from reproduction-only optical disks such as a DVD-ROM or DVD-Video, have been placed on the market. However, the 2.6 GB DVD-RAM does not respond sufficiently to the consumer""s needs in the recording capacity. This raises expectations for a 4.7 GB DVD-RAM or a 4.7 GB DVD-RW. That is, these phase change optical disks, equivalent to a DVD-Video in recording capacity, are available for use as video recording optical disks that will replace VTRs.
However, it has been pointed out that the recording by the phase-change recording method, if repeated several thousands to scores of thousands times, would degrade the reproduced signal and prevent information from being reproduced correctly (see JP-A-10-49872 disclosed on Feb. 20, 1998). The phase change recording method melts the recording film during information recording. This means that the viscosity of the melted area of the recording film decreases and that the recording film flows in some direction. This also changes the thickness in some areas in the recording film. The central level of the reproduced signal and the amplitude depend largely on the thickness of the recording film. As a result, a degradation that depends upon the thickness of the recording film occurs in the reproduced signal, causing jitters.
To solve this problem, two information recording methods have been devised (Both are described in JP-A-10-49872 described above).
One method is to shift the information recording start position by about eight bytes randomly each time information is recorded in each sector. This method shifts each two consecutive melting parts by at least eight bytes even if the same pattern information is recorded and therefore minimizes the amount of recording film flow described above. The other method is to reverse the polarity of recorded information each time information is recorded in each sector. The optical disk system described above employs the mark edge recording method. This mark edge recording method records marks (parts melted by a high-power pulse train), each having its own length, and spaces (parts created by directing a relatively low-power energy to mark-recorded parts to change them to crystallized parts) and associates the edge positions (both ends) of each mark with information. Unless the relative positions of the edges change, this method retains information even if marks and spaces are reversed. Therefore, even if the polarity is changed alternately, no problem is generated. The method repeats the cycle in which melted parts are crystallized the next time information is recorded, thus minimizing the deterioration in the reproduced signal caused by the recording film flow.
The two methods described above, which are very excellent technologies, are employed as the standard of the 2.6 GB DVD-RAM and the 4.7 GB DVD-RAM.
The prior art methods described above are very excellent. As a matter of fact, recording the same pattern of information on a 2.6 GB DVD-RAM in the method described above, if repeated about 100,000 times, gives the practically usable reproduced-signal quality. However, recording the same pattern of information on a 4.7 GB DVD-RAM in the method described above, if repeated several thousand times, results in 15% or higher jitters in the reproduced signal, possibly giving practical inconvenience. The investigation made by the inventor and the colleagues reveals at least two causes for this problem. One cause is that the amplitude of the signal reproduced from the shortest mark on the 4.7 GB DVD-RAM is 10 dB or lower than that of the 2.6 GB DVD-RAM. This is because the shortest mark of the 2.6 GB DVD-RAM is about 0.6 microns and the shortest mark of the 4.7 GB DVD-RAM is about 0.42 microns, about ⅔times shorter than that of the 2.6 GB DVD-RAM. As a result, when the thickness of the recording film changes as described above, the central amplitude level of the reproduced signal and the variation in the amplitude largely exceed the allowable range on a relative basis.
Another cause is that, even if one of the above two methods is used, one sector may include a part which is thicker or thinner than the allowable range. A careful study indicates that the flow direction of the recording film depends on the length of a recorded mark. That is, in part A, which is a part of the mark strings of a recording pattern (mark-space arrangement in one sector) in a sector, where there are many 3T marks, the recording film flows in the beginning-to-end direction of the sector . On the other hand, in part B where there are many 4T-14T marks, the recording film flows in the end-to-beginning direction in contract to the part where there are many 3T marks. As a result, depending upon the positional relation between part A and part B, the thickness of the recording film exceeds the allowable range (becomes thick or thin) in the boundary between part A and part B.
Therefore, it is a first object of the present invention to provide an information recording method and an information recording apparatus, as well as an information recording medium, that do not generate an area where the thickness of the recording film exceeds the allowable range and that minimizes the change in the central amplitude level of the reproduced signal and in the amplitude of the reproduced signal even if information is re-written more than tens of thousands times.
In addition, even if the above problem is solved, the thickness of the recording film may exceed the allowable range in the beginning and end of a sector and that part of the sector may largely degrade the reproduced signal. This condition occurs when the recording film flow may be suppressed partially but not in the whole sector. That is, when there is an average recording film flow in the whole sector (the amount of beginning-to-end direction flow of a sector does not match that of the opposite direction flow), the thickness of the recording film exceeds the allowable range in a part near the beginning or the end of the sector.
Therefore, it is a second object of the present invention to provide an information recording method and an information recording apparatus, as well as an information recording medium, that do not generate, in the beginning or end area of a sector, an area where the thickness of the recording film exceeds the allowable range and that minimize the change in the central amplitude level of the reproduced signal and in the amplitude of the reproduced signal even if information is re-written more than tens of thousands times.
(1) According to one aspect of the present invention, there is provided a method for recording information for use with an information recording medium on which a relatively-moving energy beam strikes to melt a recording film and to record marks corresponding to information, the method comprising a first step for recording a mark string of at least one dummy pattern in a predetermined position before a second step for recording a mark string of a recording pattern corresponding to original information in the predetermined position.
This method records a mark string of a dummy pattern different from that of an original pattern in the first step even when a mark string of the same original pattern must be recorded repeatedly in a predetermined position. This reduces the possibility that an area where the thickness of the recording film is changed is generated. However, even when information is recorded in the method described above, a reproduced signal degradation may occur in the beginning and end of a sector. In that case, the following information recording method should be used.
(2) According to another aspect of the present invention, there is provided the method for recording information described in (1) wherein the melting causes the recording film to flow in a relative moving direction of the information recording medium and the energy beam or in an opposite direction and the flow direction is changed in response to the mark string of an original pattern corresponding to the original information and/or the mark string of the dummy pattern and wherein, in the first step, the mark string of the dummy pattern whose average recording film flow direction is different from that of the original pattern recorded in the second step is recorded at least before the second step.
This method prevents an average recording film flow in the whole sector, minimizing the amount of degradation of the reproduced signal in the beginning and end of a sector. For example, when the recording of an original pattern causes the recording film to flow from the end to the beginning of the sector in the second step, the mark string of a dummy pattern causing the recording film to flow from the beginning to the end should be recorded in the first step. In addition, recording a mark string of two dummy patterns, as described below, allows the recording film flow direction to be controlled more precisely.
(3) According to another aspect of the present invention, there is provided the method for recording information described in (1) wherein the melting causes the recording film to flow in a relative moving direction of the information recording medium and the energy beam or in an opposite direction and the flow direction is changed in response to the mark string of the dummy pattern and wherein, in the first step, the mark strings of at least two dummy patterns are recorded at least before the second step, at least two dummy patterns having different average recording film flow directions.
When doing mark edge recording, a mark string of recording patterns corresponding to information including marks with different lengths is recorded. The inventor and the colleagues have revealed that, in such a case, the recording film flow direction depends on the mark length and that the recording film flows from the beginning to the end of the sector or from the end to the beginning of the sector depending upon the mark length. In addition, they have revealed that average recording film flow direction depends on the existence probability of marks of various lengths. Furthermore, they have revealed that the recording film flow direction may be controlled more efficiently in the first step by separately recording a dummy pattern including marks causing the recording film to flow from the beginning to the end of the sector and a dummy pattern including marks causing the recording film to flow from the end to the beginning of the sector. That is, the following information recording method is excellent.
(4) According to another aspect of the present invention, there is provided the method for recording information described in (3) wherein, in the second step, the information is recorded on the information recording medium as a plurality of marks each with its own length and a plurality of spaces (areas between two marks) each with its own length, the melting causes the recording film to flow in the relative moving direction of the information recording medium and the energy beam or in the opposite direction, and the flow direction is changed in response to the mark length and wherein, in the first step, the mark strings of at least two dummy patterns are recorded, each of the mark strings including a first mark group causing the recording film to flow in the relative moving direction and a second mark group causing the recording film to flow in an direction opposite to the relative moving direction.
It is desired that the mark string of a dummy pattern be recorded three or four times immediately before the mark string of an original pattern is recorded. However, if the time required for the first step exceeds the allowable range, the mark string of a dummy pattern may be recorded once or twice immediately before the mark string of an original pattern is recorded. In this case, because the dummy patterns are limited to one or two types, they may be randomly or sequentially selected from several types of dummy patterns and recorded.
(5) According to another aspect of the present invention, there is provided the method for recording information described in (1) wherein there are plurality of mark strings of dummy patterns and, from the mark strings of the plurality of dummy patterns, the mark strings of dummy patterns are selected randomly or sequentially for recording in the first step.
In the case of 4.7 GB DVD-RAM, for example, there is an area, such as the defect management area, where the original pattern is likely to be the same in most cases. Therefore, it is more efficient to use the method described above only when information is recorded in such an area.
(6) According to another aspect of the present invention, there is provided the method for recording information described in (1) wherein the predetermined position is a non-user data area such as a defect management area and a user data management area.
The first mark group and the second mark group may depend on the structure of the information recording medium or on the modulated waveform (recorded waveform) of the energy beam intensity for recording marks. In such a case, dummy pattern information and/or recording waveforms suited for the information recording medium should be recorded on the information recording medium as described below.
(7) According to another aspect of the present invention, there is provided the recording information medium for use in the method described in (1), wherein the medium has an area where information on the dummy pattern is recorded.
To implement the method for recording information described in (1), an apparatus for recording information described below is suitable.
(8) According to another aspect of the present invention, there is provided an apparatus for recording information for implementing the method for recording information described in (1), comprising an energy beam generator; an information recording medium moving unit which relatively moves the information recording medium and the energy beam; and a dummy pattern generator which generates the dummy patterns for use in the first step.
(9) According to another aspect of the present invention, there is provided the apparatus for recording information described in (8), further comprising a dummy pattern selector which randomly or sequentially selects the dummy patterns generated by the dummy pattern generator.
(10) According to another aspect of the present invention, there is provided the apparatus for recording information described in (8), further comprising a dummy pattern reproducer which reproduces dummy pattern information recorded on the information recording medium; and a dummy pattern transmitter which transmits the dummy pattern information to the dummy pattern generator.